It is quite common for eyeglasses to fall from the wearer and break. This can also happen during sports activities and the like when force is applied against the glasses which causes the lens to break or become scratched. Typically, when this happens, one has to replace the eye wear entirely which is costly.
Further, many people have multiple eyeglasses. One might be used for reading while the other is used for driving or viewing distances. One might be used as sunglasses to decrease light intensity to the eyes, while another is used for indoor and less bright scenarios.
What is needed is a way to be able to change out or replace a lens with another, when one becomes scratched, broken, or undesirable for the present circumstances. At present, very small screws are often used along with guide wires and precise placement of very small pieces which make changing lenses very difficult. A skilled professional is often required, and though the frames often remain perfectly fine, they have to be thrown out with the lenses because new lenses are no longer made to the specification of the old frames, or would require the wearer go without frames for a period of time. The latter is problematic, because most people who wear glasses need them to function each day.